Icing of the engine commonly occurs during flight through clouds containing supercooled water droplets or during ground operation in freezing fog. Ice can accumulate on the intake leading edge, the fan spinner, the fan blades and even further into the engine. Ice tends to form first on the leading edges of components, altering the airflow, reducing lift, increasing drag and adding weight. Relatively small amounts of ice can have a disproportionate effect on aircraft performance. Additionally, damage may result from ice breaking away and being ingested into the engine or hitting the acoustic material lining the intake duct.
Anti-icing operations are conducted to prevent the bonding of snow and ice to the component surfaces. Once bonded snow or ice has formed, de-icing operations are conducted to remove it. Conventional anti-icing and de-icing systems use hot air, bled from a compressor and ducted to the areas of the engine requiring de-icing, or electrical heating of the parts concerned; sometimes a combination of the two is used. Other known systems have used ducted hot oil, microwaves or chemical de-icing means.
A disadvantage of known anti-icing and de-icing systems is that they require additional hardware, in the form of bleeds and ducting for hot air, or heating elements and their associated control systems, which add weight and complexity to the engine. In addition, the need for warmed and pressurised air, or for electrical power, is detrimental to the overall performance of the engine and reduces its efficiency.
Many components of gas turbine engines are subjected to vibration in use. Not only the rotating compressor and turbine blades, but also static components such as guide vanes and nacelles, are subjected to vibrations which reduce the fatigue lives of these components and which can lead to premature cracking if the amplitude of vibration is sufficiently large.
It is known to use various methods to damp these vibrations, in which the vibrational energy is converted into another form of energy. Generally, heat is produced as a by-product of the damping process. In the design of gas turbine engines, such heat is conventionally regarded as undesirable, or its effects are ignored altogether.
There is increasing interest in forming fan blades for gas turbine engines from composite materials. This offers several advantages, among which are weight saving and the ability to tailor the mechanical properties of a blade, for example in different directions. However, ice adhesion to composite materials is not well understood, and composite materials are generally not good conductors of heat. Existing de-icing and anti-icing methods may not, therefore, be readily applicable to composite blades.